Get group identity
#include <unistd.h>
#include <sys/types.h>
gid_t getgid(void);
gid_t getegid(void);
getgid() returns the real group ID of the calling process.
getegid() returns the effective group ID of the calling process.
These functions are always successful.
POSIX.1-2001, 4.3BSD.
The original Linux getgid() and getegid() system calls supported only 16-bit group IDs. Subsequently, Linux 2.4 added getgid32() and getegid32(), supporting 32-bit IDs. The glibc getgid() and getegid() wrapper functions transparently deal with the variations across kernel versions.
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